docs: def _ssweek_info(ssweek_year, ssweek_week):
      "Give all the ssweek info we need from one calculation"
      prev_year_start = _ssweek_year_start(ssweek_year-1)
      year_start = _ssweek_year_start(ssweek_year)
      next_year_start = _ssweek_year_start(ssweek_year+1)
      first_day = year_start + dt.timedelta(weeks=ssweek_week-1)
      last_day = first_day + dt.timedelta(days=6)
      prev_year_num_weeks = ((year_start - prev_year_start).days) // 7
      year_num_weeks = ((next_year_start - year_start).days) // 7
      return (first_day, last_day, prev_year_num_weeks, year_num_weeks)